Method and node for controlling an uplink noise figure and gain

ABSTRACT

The disclosure relates to a method for controlling an uplink noise figure and gain in a distributed antenna system network comprising at least one intermediate radio unit and one or more remote radio heads connected via a respective link to the at least one intermediate radio unit. The method comprises: establishing a target noise figure, an adjusting, for each link between the one or more remote radio heads and the intermediate radio unit, attenuation such as to obtain the target noise figure for each remote radio head connected to the at least one intermediate radio unit. The disclosure also relates to corresponding distributed antenna system network, devices, computer programs, and computer program products.

TECHNICAL FIELD

The technology disclosed herein relates generally to the field ofdistributed antenna system networks and in particular to method andnodes for controlling an uplink noise figure and gain in such networks.

BACKGROUND

In a distributed antenna system network a number of antennas aredistributed geographically to cover a geographic area (a cell), eachantenna covering a particular part thereof. The distributed antennasystem is typically deployed in an indoor environment and uses a ratherlow transmission power. The antennas, also denoted remote radio heads inthe following, are all connected by means of a respective cable to aradio unit, which thus receives signals from and transmits signals tothe various remote radio heads. The single radio unit (or radio basestation) may thus provide coverage e.g. in different parts of abuilding, each part having a properly placed remote radio head. Acommunication device can then move between the coverage of the differentremote radio heads while staying within the same cell.

A communication device located at a downlink (DL, the direction frombase stations to the communication device) cell border between thecoverage of the distributed antenna system network and the coverage of ahigh transmission power network node (e.g. base station of a macro cell)will be at the point where it receives signaling from both cells withapproximately the same strength. At this cell border, there may be alarge difference between the DL transmission power sent from the remoteradio head on the one hand and the DL transmission power sent from thebase station of the macro cell on the other hand. The communicationdevice, receiving signaling from both cells with approximately samestrength, will then be much closer to the remote radio head than to thebase station of the macro cell.

At this downlink cell border, the uplink (UL, the direction from thecommunication device to the base stations) path loss is much lower tothe remote radio head than to the base station of the macro cell. Thismeans that the radio unit cell will be dominating the power control ofthe communication device. This leads to the UL power being regulateddown to a level that is suitable for the remote radio unit cell, butthat is much too low for the macro cell.

This UL/DL imbalance leads to problems e.g. in view of soft handover,and also e.g. if the macro cell provides a high-speed downlink packetaccess (HSDPA) service to the communication device, since the macro cellwill, in this scenario, have difficulties receiving a high-speeddedicated physical control channel (HS-DPCCH), which is only decoded inthe serving cell (i.e. in the macro cell providing the DL HS service).The HSDPA throughput for the communication device will thus suffer.Still another problem is the ability of the communication devices toperform a successful random access.

SUMMARY

An object of the present disclosure is to solve or at least alleviate atleast one of the above mentioned problems.

The object is according to a first aspect achieved by a method forcontrolling an uplink noise figure and gain in a distributed antennasystem network comprising at least one intermediate radio unit and oneor more remote radio heads connected via a respective link to the atleast one intermediate radio unit. The method comprises establishing atarget noise figure, and adjusting, for each link between the one ormore remote radio heads and the intermediate radio unit, attenuationsuch as to obtain the target noise figure for each remote radio headconnected to the at least one intermediate radio unit.

The method provides a way of making the length of the links (cables)between different remote radio heads and an intermediate radio unit toappear to be the same, by providing an active adjustment of theattenuation. Thereby the method overcomes problems related to unbalanceduplink/downlink. Further, the method solves a problem of a large spreadin noise figure and gain of the various remote radio heads, which renderthe setting of a correct thermal noise floor and gain difficult. Stillfurther, the method reduces the effects of attenuation in a cableincreasing rapidly with respect to frequency owing to the adjustment ofthe attenuation so that all links obtain essentially the same targetnoise figure.

The object is according to a second aspect achieved by a distributedantenna system network comprising at least one intermediate radio unitand one or more remote radio heads connected via a respective link tothe at least one intermediate radio unit. The distributed antenna systemnetwork is configured for controlling an uplink noise figure andcomprises at least one processor; and at least one memory storinginstructions that, when executed by the at least one processor, causesthe distributed antenna system network: establish a target noise figure,and adjust, for each link between the one or more remote radio heads andthe intermediate radio unit, attenuation such as to obtain the targetnoise figure for each remote radio head connected to the at least oneintermediate radio unit.

The object is according to a third aspect achieved by a device of adistributed antenna system network. The device is configured forcontrolling an uplink noise figure and comprises at least one processor;and at least one memory storing instructions that, when executed by theat least one processor, causes the device to: establish a target noisefigure, and adjust, for a link between a remote radio head and anintermediate radio unit, attenuation such as to obtain the target noisefigure for the remote radio head connected to the intermediate radiounit.

The object is according to a fourth aspect achieved by a computerprogram for a device of a distributed antenna system network. The deviceis configured for adapting an uplink noise figure. The computer programcomprises computer program code, which, when run on the device causesthe device to: establish a target noise figure, and adjust, for a linkbetween a remote radio head and an intermediate radio unit, attenuationsuch as to obtain the target noise figure for the remote radio headconnected to the intermediate radio unit.

The object is according to a fifth aspect achieved by a computer programproduct comprising a computer program as above, and a computer readablemeans on which the computer program is stored.

The object is according to a sixth aspect achieved by a device of adistributed antenna system network comprising first means forestablishing a target noise figure. The device comprises second meansfor adjusting, for a link between a remote radio head and anintermediate radio unit, attenuation such as to obtain the target noisefigure for the remote radio head connected to the intermediate radiounit.

Further features and advantages of the present disclosure will becomeclear upon reading the following description and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates, in an aspect of the present disclosure, an exampleof how to obtain same uplink attenuation on all cables.

FIG. 2 illustrates schematically an embodiment of a distributed antennasystem network of an aspect of the present disclosure.

FIG. 3 illustrates an intermediate radio unit.

FIG. 4 illustrates schematically an embodiment of a distributed antennasystem network of an aspect of the present disclosure.

FIG. 5 illustrates schematically an embodiment of a distributed antennasystem network of an aspect of the present disclosure.

FIG. 6 illustrates schematically an embodiment of a distributed antennasystem network of an aspect of the present disclosure.

FIG. 7 illustrates a flow chart over steps of a method in a distributedantenna system network in accordance with the present disclosure.

FIG. 8 illustrates schematically a device of a distributed antennasystem network and means for implementing methods of the presentdisclosure.

FIG. 9 illustrates a flow chart over steps of a method in a distributedantenna system network in accordance with the present disclosure.

FIG. 10 illustrates a device of a distributed antenna system networkcomprising function modules/software modules for implementing methods ofthe present disclosure.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth such as particulararchitectures, interfaces, techniques, etc. in order to provide athorough understanding. In other instances, detailed descriptions ofwell-known devices, circuits, and methods are omitted so as not toobscure the description with unnecessary detail. Same reference numeralsrefer to same or similar elements throughout the description.

In an aspect, the present disclosure provides a solution to theunbalanced UL/DL problem by applying desensitizing on the UL to make theremote radio heads less dominant in the UL (compared to the macro cell).The macro base station will thereby receive a better UL signal. Thedesensitizing function is, in an aspect, implemented in an intermediateradio unit (IRU) of a distributed antenna system network.

The remote radio heads are located at different distances from theintermediate radio unit and the cable lengths from the intermediateradio unit to the remote radio heads thus differ. This difference incable length means that the attenuation in the cables will vary verymuch. The attenuation and noise figure (NF) being different for thedifferent remote radio head branches means that it is difficult to set asuitable noise floor and gain. Therefore, in an aspect, this is overcomeby setting the attenuation of links between the remote radio heads andthe intermediate radio unit such as to be equal for all remote radioheads. However, this will affect the noise of the remote radio headbranches, and the present disclosure provides, in an aspect, a solutionalso for this.

The noise factor (F) of a device of a radio frequency signal chain, ormore generally of a system, is defined as the ratio of the inputsignal-to noise (SNR) and the output SNR:

$F = \frac{{SNR}_{IN}}{{SNR}_{OUT}}$

The noise figure (NF) if the noise factor expressed in decibels (dBs):

$\begin{matrix}{{NF} = {10\mspace{14mu} \log \mspace{11mu} (F)}} \\{= {10\mspace{14mu} \log \mspace{11mu} \left( \frac{{SNR}_{IN}}{{SNR}_{OUT}} \right)}} \\{= {{SNR}_{{IN},{dB}} - {SNR}_{{OUT},{dB}}}}\end{matrix}$

The noise figure, NF, is thus expressed in dB, while the noise factor,F, is a linear correspondent (i.e. NF is F expressed in dBs). The totalnoise factor F of a radio frequency chain can be expressed by Friis'Formula:

${F_{tot} = {{F\; 1} + \frac{{F\; 2} - 1}{G\; 1} + \frac{{F\; 3} - 1}{G\; 1\; G\; 2} + \ldots}}\mspace{14mu},$

where F_(n) is the noise factor for the n^(th) device and G_(n) is thepower gain of the n^(th) device. The performance of e.g. a remote radiohead can be expressed by the NF.

FIG. 1 illustrates a distributed antenna system network 1 of the presentdisclosure and an example of how to obtain same uplink attenuation onall links (irrespective of cable lengths) between the intermediate radiounit (IRU) and the various remote radio heads. Depending on how thesystem is modeled and how the antenna reference point is chosen, theNF_(tot) can vary considerably. The reference point could for example bechosen to be just before the IRU 2 ₁ of the distributed antenna system1, illustrated at reference point denoted A. Alternatively, thereference point could be chosen to be at the remote radio head 3 ₂having the shortest cable as illustrated at reference point denoted B.These alternatives, as well as other alternatives, have their advantagesas well as disadvantages. However, in the present disclosure, the ULattenuation is set to be equal for all remote radio heads 3 ₁, 3 ₂. Theremote radio head 3 ₁ having the longest cable and thus presumably thehighest attenuation (since the same type of cables are typically usedfor all links) is the uppermost remote radio head in the figure. Thereference point denoted C is then set as the uplink antenna referencepoint. In order for all links from the IRU to the remote radio heads tohave same attenuation, the attenuation to the lowermost remote radiohead 3 ₂ may be adjusted by a variable attenuator, such as to be equalto the attenuation of the longest cable (i.e. the cable to the uppermostremote radio head 3 ₁). In the particular example illustrated, the cableattenuation of the first cable 4 ₁ to the first remote radio head 3 ₁ is30 dB, while the cable attenuation of the second cable 4 ₂ to the secondremote radio head 3 ₂ is 10 dB. The variable attenuator of the secondremote radio head 3 ₂ is therefore set to 20 dB, giving the sameattenuation between the IRU 2 ₁ to the first and second remote radioheads 3 ₁, 3 ₂. It is noted that instead of a variable attenuator, avariable gain stage could instead be used, i.e. reducing gain instead ofincreasing attenuation, or vice versa depending on need of the links.

The fact that the attenuation from the IRU 2 ₁ to the first and secondremote radio heads 3 ₁, 3 ₂ is equal (and for all other remote radioheads, not illustrated) will provide a good antenna reference point. Forexample, the UL/DL imbalance to a neighboring macro cell depends on thelargest cable length, and all communication devices will have a correctinitial transmission power. A first communication device, denoted UE1,communicating via the first remote radio head 3 ₁, and a secondcommunication device, denoted UE2, communicating via the second remoteradio head 3 ₂, will have the same UL pathloss.

FIG. 2 illustrates schematically an embodiment of a distributed antennasystem network 1 of an aspect of the present disclosure. The distributedantenna system network 1 comprises a number of intermediate radio units(IRUs) 2 ₁, 2 ₂, . . . , 2 _(m) each connected to a control unit 5. TheIRUs 2 ₁, 2 ₂, . . . , 2 _(m) (described more in detail with referenceto FIG. 3) are also each connected to a number of remote radio heads.For example, a first port A of a first IRU 2 ₁ is connected to theremote radio heads 3 ₁, 3 ₂, . . . , 3 _(n) via a respective link 4 ₁, 4₂, . . . , 4 _(n), the link comprising a cable able to distributecarriers to the remote radio heads on an intermediate frequency (IF).The first IRU 2 ₁ may comprise further such ports, e.g. a second port Bconnected to the remote radio heads 3 ₁, 3 ₂, . . . , 3 _(n) via arespective link (cable), as illustrated by dashed lines, the first linkindicated at reference numeral 4B₁. As a particular example, each portA, B of each IRU 2 ₁, 2 ₂, . . . , 2 _(m) may be connected to eightremote radio heads 3 ₁, 3 ₂, . . . , 3 ₈.

The remote radio head 3 ₁, 3 ₂, . . . , 3 _(n) receives an UL radiofrequency (RF) signal from a communication device (not illustrated) anddownconverts the UL RF signal to an intermediate frequency (IF) signaland sends it over the link 4 ₁, 4 ₂, . . . , 4 _(n) to the IRU 2 ₁. Inthe DL, the remote radio head 3 ₁, 3 ₂, . . . , 3 _(n) receives IFsignals from the IRU 2 ₁, and correspondingly upconverts the IF signalsto RF signals for transmission over an air interface to thecommunication devices.

By using IF over the links 4 ₁, 4 ₂, . . . , 4 _(n) instead of RF,cheaper cables with high RF attenuation may be used, such as forinstance standardized cables for Ethernet, e.g. enhanced category 5cable (CAT5e), CAT6 or CAT7 cables.

FIG. 3 illustrates the intermediate radio unit 2 ₁ in some more detail.The IRU 2 ₁ may thus comprise e.g. two ports, port A and port B (alsodenoted branches A and B), each comprising transmitter circuitry (TX A,TX B) and receiving circuitry (RX A, RX B). In the figure, thetransmitter circuitry TX A and receiving circuitry RX A for port A areencircled and denoted TRX A, and correspondingly the transmittercircuitry TX B and receiving circuitry RX B for port B are encircled anddenoted TRX B. Each port A, B is, as mentioned, connected to a number ofremote radio heads. In the illustrated case, each of the two ports A, Bare connected to eight remote radio heads 3 ₁, 3 ₂, . . . , 3 ₈ (theremote radio heads not illustrated in this figure), but it is noted thatthe number of ports and the number of remote radio heads may be higheror lower as well. The IRU 2 ₁ thus comprises an interface towards theremote radio heads 3 ₁, 3 ₂, . . . , 3 _(n) (denoted RRH Interface inthe figure). In the illustrated case there may be a link between a firstremote radio head 3 ₁ (of the eight remote radio heads) and theintermediate radio unit 2 ₁, and in particular between an input (denotedTX/RX A/B 1 in the figure) of the intermediate radio unit 2 ₁ whichinput corresponds to the first remote radio head 3 ₁. This link, inparticular this cable, may comprise a number of twisted pairs, each paircomprising two wires carrying signals. In the illustrated case, only twosuch pairs would be needed (one for port A and one for port B), and anyadditional pairs could be used e.g. for powering the remote radio heads.It is however noted that such power could be fed on the same pairs asthe IF signals.

In this case, each remote radio head 3 ₁, 3 ₂, . . . , 3 ₈ may beconfigured to support two RF branches, i.e. branch to port A and branchto port B. Each remote radio head 3 ₁, 3 ₂, . . . , 3 ₈ may howeversupport multiple antenna branches. The multiple antenna branches of aremote radio head can, in an aspect of the disclosure, be individuallycontrolled. The signals conveyed to the IRU from two such antennabranches of the remote radio head may experience different attenuatione.g. since cable attenuation can be slightly different between pairs ofwires in the same link (cable) (the signals being conveyed on differentsuch wire pairs).

The IRU 2 ₁ may comprise further components and circuitry, such asamplifiers, a radio controller, synchronization devices, switches,Frequency-shift keying (FSK) modems, line transforms and overvoltageprotection devices etc. Such components and circuitry are schematicallyindicated by empty boxes.

In an aspect of the present disclosure, a target noise figure is setwhich should be obtained by all the remote radio heads 3 ₁, 3 ₂, . . . ,3 _(n). This can be accomplished by adjusting the UL attenuation of thelinks individually so that all the remote radio heads 3 ₁, 3 ₂, . . . ,3 _(n) indeed obtain the target noise figure. The attenuation may beadjusted in the remote radio heads, and/or in the IRU 2 ₁. A remoteradio head with a cable having a low attenuation (i.e. remote radio headbeing close to the IRU) may need to add much attenuation, e.g. by usinga variable attenuator, to reach the target noise figure. Another remoteradio head may need to add attenuation beyond the capability of thevariable attenuator thereof, and additional noise could then be added atthe corresponding port of the IRU. Various embodiments in this respectare described in the following with reference to FIGS. 4, 5 and 6.

FIG. 4 illustrates schematically an embodiment of a distributed antennasystem network 1, and in particular the remote radio heads 3 ₁, 3 ₂, . .. , 3 _(n) and the IRU 2 ₁. Each remote radio head 3 ₁, 3 ₂, . . . , 3_(n) comprises a variable attenuator 6 ₁, 6 ₂, . . . , 6 _(n) and anamplifier 7 ₁, 7 ₂, . . . , 7 _(n), which may be a variable-gainamplifier as illustrated in the figure. The remote radio heads 3 ₁, 3 ₂,. . . , 3 _(n) may also or alternatively comprise a variable gain stage(not illustrated) for reducing or increasing gain on the links 4 ₁, 4 ₂,. . . , 4 _(n). Each remote radio head 3 ₁, 3 ₂, . . . , 3 _(n) alsocomprises an antenna device 8 ₁, 8 ₂, . . . , 8 _(n) for receivingsignaling from and transmitting signaling to communication deviceswithin their coverage. The IRU 2 ₁, which is schematically illustratedin FIG. 4, comprises an interface 9 towards the remote radio heads 3 ₁,3 ₂, . . . , 3 _(n) (reference is made to FIG. 3 for details thereof),for receiving the uplink signals from the remote radio heads 3 ₁, 3 ₂, .. . , 3 _(n) (and sending downlink signals to the remote radio heads 3₁, 3 ₂, . . . , 3 _(n)). For the uplink communication, the remote radioheads may downconvert a received uplink (RF) signal to IF, as mentionedearlier, and send it over its link to the IRU 2 ₁. The signals arecombined (in a combiner) and processed further. Such further signalprocessing may comprise extracting received IF signals and forward themto a receiver back-end, which downconverts the signals from IF to ananalogue baseband signal which is further filtered and digitized. Suchreceiver back-end may send combined received signals in digital form tothe baseband module for further processing such as demodulation,decoding etc. as known in the art per se. Alternatively, the received IFsignals could be sampled directly (i.e. sampled on IF) and then bedigitally downcoverted.

The IRU 2 ₁ may further comprise an amplifier 10, e.g. a variable-gainamplifier comprising a noise source 10 a for noise injection. By addingnoise to a signal combined in the IRU 2 ₁ the noise figure for branchesconnected to the IRU 2 ₁ be increased if needed. This can thus beaccomplished by using the variable-gain amplifier 10, which may comprisean analog amplifier or a digital amplifier. FIG. 5 illustratesschematically an embodiment of a distributed antenna system network 1 ofan aspect of the present disclosure. The difference in this embodimentcompared to the embodiment of FIG. 4, is that the IRU 2 ₁ comprisesvariable-gain amplifiers 11 ₁ and 11 ₂ for each input of the IRU 2 ₁.That is, a variable-gain amplifier is provided for each remote radiohead (before combination of signals), in contrast to the embodiment ofFIG. 4, wherein the variable-gain amplifier is adding noise aftercombination of the signals received at the different remote radio heads.

FIG. 6 illustrates schematically an embodiment of a distributed antennasystem network 1 of an aspect of the present disclosure. In variousembodiments, the IRU 2 ₁ may be adapted to handle frequency bandspecific noise or carrier specific noise. For example, the IRU 2 ₁ maycomprise filters 12 ₁, 12 ₂, e.g. bandpass filters, in the uplinkdirection from the remote radio heads located before the variable-gainamplifier 11 ₁, 11 ₂, such as to filter out a specific frequency bandfor which noise is added. However, in other embodiments, the filters 12₁, 12 ₂, are omitted, and a filter 13, preferably a configurable filter,is provided. The filter 13 may be provided in connection with theamplifier 10, in the figure the filter 13 is illustrated as connectedbetween the amplifier 10 and the interface (combiner) 9, but such filter13 could alternatively be placed before the amplifier 10 (i.e. feedingthe amplifier with signals instead of vice versa). The purpose of thefilter 13 is to ensure that added noise is limited to only a part of theIF band, e.g. where there is a WCDMA carrier, while blocking noise forother parts of the IF band where there may be signals not needingdesensitization (e.g. LTE). As a particular example, if the distributedantenna system network 1 is used for both WCDMA and LTE communication,e.g. having WCDMA at 40-50 MHz and LTE at 60-70 MHz, then the filter 13should be configured to have a passband of 40-50 MHz and stopband from60 MHz.

FIG. 7 illustrates a flow chart over steps of a method in a distributedantenna system network 1 in accordance with the present disclosure. Themethod 20 for controlling an uplink noise figure and gain may beimplemented in a distributed antenna system network 1 such as thenetworks 1 that have been described with reference to FIGS. 2-5. Thedistributed antenna system network 1 comprises at least one intermediateradio unit 2 ₁ and one or more remote radio heads 3 ₁, 3 ₂ connected viaa respective link 4 ₁, 4 ₂ to the at least one intermediate radio unit 2₁. The method 20 may be implemented in the intermediate radio unit 2 ₁,in the remote radio heads 3 ₁, 3 ₂, or in a control unit 5. The method20 may alternatively be implemented in a distributed manner within thedistributed antenna system network 1, wherein two or more devicesperform one or more functions.

The method 20 comprises establishing 21 a target noise figure. It isnoted that the noise figure and noise factor are the same “noisemeasure” expressed in decibel (dB) and expressed in linear scale,respectively, and that the establishing could equally well beestablished in the linear scale. The target noise figure may be aconfigurable parameter that may be set by the operator of thedistributed antenna system network 1. The establishing 21 may forinstance comprise retrieving the target noise figure from a database. Asanother example, if the method 20 is implemented in the intermediateradio unit 2 ₁, the intermediate radio unit 2 ₁ may be configured toreceive the target noise figure from the control unit 5, theestablishing 21 thus comprising receiving in the intermediate radio unit2 ₁ the target noise figure from the control unit 5.

The method 20 comprises adjusting 23, for each link 4 ₁, 4 ₂ between theone or more remote radio heads 3 ₁, 3 ₂ and the intermediate radio unit2 ₁, attenuation such as to obtain the target noise figure for eachremote radio head 3 ₁, 3 ₂ connected to the at least one intermediateradio unit 2 ₁. The attenuation may be adjusted, e.g. added to, in theintermediate radio unit 2 ₁, for each port A, B, or the attenuation maybe added in each remote radio head 3 ₁, 3 ₂, or the attenuation may beadjusted in both the remote radio head 3 ₁ and the intermediate radiounit 2 ₁. It is thus noted that the attenuation may be adjusted anywherein the signal chain from the reception of the signal at an antenna ofthe remote radio head 3 ₁ to the intermediate radio unit 3 ₁. As aparticular example, if the target noise figure is set to a high value,the attenuation could be adjusted where the signal has the lowest power,which typically is close to the antenna receiving the signal, and theattenuation could thus be adjusted in the remote radio head 3 ₁.

In an embodiment, the establishing 21 the target noise figure comprises:

-   -   measuring in each remote radio head 3 ₁, 3 ₂ a respective cable        attenuation and reporting it to the intermediate radio unit 2 ₁,    -   establishing, in the intermediate radio unit 2 ₁, the highest        cable attenuation among the received reports about measured        cable attenuations, and    -   establishing 21 the target noise figure to be equal to a noise        figure corresponding to the noise figure of the link 4 ₁, 4 ₂        having the highest cable attenuation.

In an embodiment, the establishing 21 the target noise figure comprises:

-   -   measuring in the intermediate radio unit 2 ₁ a respective cable        attenuation,    -   establishing, in the intermediate radio unit 2 ₁, the highest        cable attenuation among the measured cable attenuations, and    -   establishing 21 the target noise figure to be equal to a noise        figure corresponding to the noise figure of the link 4 ₁, 4 ₂        having the highest cable attenuation.

From the above two embodiments it is clear that cable attenuationmeasurements may be performed in either the intermediate radio unit orin the remote radio head. Yet another alternative to determine the cableattenuation is to perform echo measurement. That is, one side, e.g. theintermediate radio unit, transmits for instance a time pulse along thecable to the remote radio head, and determine the cable attenuationbased on analysis of reflected signals together with knowledge aboutcable termination impedance in the remote radio head. In an embodiment,the method 20 comprises after the establishing 21 of the target noisefigure and before the adjusting 2 ₃ (see FIG. 7):

-   -   determining 22, for each remote radio head 3 ₁, 3 ₂, whether the        established target noise figure can be fulfilled for the        respective remote radio head 3 ₁, 3 ₂.

In a variation of the above embodiment, the adjusting 23 comprises forthe case of each of the one or more remote radio heads 3 ₁, 3 ₂ beingable to fulfil the target noise figure:

-   -   adjusting 23, in each remote radio head 3 ₁, 3 ₂, attenuation        such as to obtain the target noise figure.

In another variation of the above embodiment, the method 20 comprisesfor the case of one or more remote radio heads 3 ₁, 3 ₂ being unable tofulfil the target noise figure:

-   -   setting, in each remote radio head 3 ₁, 3 ₂ unable to fulfil the        target noise figure, the attenuation of a variable attenuator 6        ₁, 6 ₂ such as to obtain a maximum achievable attenuation, and    -   adding, in the intermediate radio unit 2 ₁, additional noise        such as to obtain the target noise figure.

In a variation of the above embodiment, the adjusting comprises addinggenerated frequency band specific noise.

In an embodiment, the method 20 comprises for the case of one or moreremote radio heads 3 ₁, 3 ₂ being unable to fulfil the target noisefigure:

-   -   sending, from the remote radio head 3 ₁, 3 ₂ being unable to        fulfil the target noise figure, a message to the intermediate        radio unit 2 informing about this inability.

In an embodiment, the establishing 21 of the target noise figure isperformed in a control unit 5, e.g. by an operator setting the targetnoise figure and the noise figure being signaled to the intermediateradio unit. In another embodiment the establishing 21 is performed inthe intermediate radio unit 2 ₁, e.g. by receiving from the control unit5 the target noise figure.

In an embodiment, the method 20 is performed in the one or more remoteradio heads 3 ₁, 3 ₂ and the establishing 21 the target noise figurecomprises receiving, from a control unit 5 or from the an intermediateradio unit 2 ₁, the target noise figure.

In another embodiment, the method is performed in the distributedantenna system network 1. That is, the steps of the various embodimentsof the method 20 may be performed in different parts (i.e. differentdevices) of the distributed antenna system network 1.

In an embodiment, the uplink noise figure and gain is controlled byadapting the uplink noise figure and gain in view of the number ofactive remote radio heads 3 ₁, 3 ₂.

In an embodiment, the adjusting 23 is performed such as to obtain thetarget noise figure and linearity for each remote radio head 3 ₁, 3 ₂connected to the at least one intermediate radio unit 2 ₁. Thegain/attenuation of each link may be adjusted in order to obtain anumber of target parameters, however comprising at least the noisefigure (i.e. noise figure being one such target parameter). Thesensitivity of a radio receiver performance is limited by noise figureand large signals by linearity.

The method 20 thus provides an advantage in that it enables to obtain atarget noise figure and gain for each link between the intermediateradio unit and the remote radio heads, even when the conditions change.For example, if only a subset of all the remote radio heads is used atparticular time, then the method automatically adjusts the attenuationsuch as to obtain same attenuation for all links. This is true also fore.g. changes in cabling (e.g. some cabling being exchanged or somecables being prolonged or shortened e.g. since a remote radio head ismoved). The method 20 may thus continuously and automatically andwithout intervention of the operator adapt the target noise figure andgain in view of such changes, e.g. change in number of active remoteradio heads.

A distributed antenna system network 1 is provided comprising at leastone intermediate radio unit 2 ₁ and one or more remote radio heads 3 ₁,3 ₂ connected via a respective link 4 ₁, 4 ₂ to the at least oneintermediate radio unit 2 ₁. The distributed antenna system network 1 isconfigured for controlling an uplink noise figure and comprises:

at least one processor 30, 40; andat least one memory 31, 41 storing instructions that, when executed bythe at least one processor 30, 40, causes the distributed antenna systemnetwork 1:

-   -   establish a target noise figure, and    -   adjust, for each link 4 ₁, 4 ₂ between the one or more remote        radio heads 3 ₁, 3 ₂ and the intermediate radio unit 2 ₁,        attenuation such as to obtain the target noise figure for each        remote radio head 3 ₁, 3 ₂ connected to the at least one        intermediate radio unit 2 ₁.

In an embodiment, the distributed antenna system network 1 is operativeto establish the target noise figure by:

-   -   measuring in each remote radio head 3 ₁, 3 ₂ a respective cable        attenuation and reporting it to the intermediate radio unit 2 ₁,    -   establishing, in the intermediate radio unit 2 ₁, the highest        cable attenuation among the received reports about measured        cable attenuations, and    -   establishing 21 the target noise figure to be equal to a noise        figure corresponding to the noise figure of the link 4 ₁, 4 ₂        having the highest cable attenuation.

In an embodiment, the distributed antenna system network 1 is operativeto establish the target noise figure by:

-   -   measuring in the intermediate radio unit 2 ₁ a respective cable        attenuation,    -   establishing, in the intermediate radio unit 2 ₁, the highest        cable attenuation among the measured cable attenuations, and    -   establishing 21 the target noise figure to be equal to a noise        figure corresponding to the noise figure of the link 4 ₁, 4 ₂        having the highest cable attenuation.

In an embodiment, the distributed antenna system network 1 is operativeto, after the establishing 21 of the target noise figure and before theadjusting 23:

-   -   determine, for each remote radio head 3 ₁, 3 ₂, whether the        established target noise figure can be fulfilled for the        respective remote radio head 3 ₁, 3 ₂.

In a variation of the above embodiment, the distributed antenna systemnetwork 1 is operative to adjust, for the case of each of the one ormore remote radio heads 3 ₁, 3 ₂ being able to fulfil the target noisefigure, by:

-   -   adjusting, in each remote radio head 3 ₁, 3 ₂, attenuation such        as to obtain the target noise figure.

In another variation of the above embodiment, the distributed antennasystem network 1 is operative to adjust, for the case of one or moreremote radio heads 3 ₁, 3 ₂ being unable to fulfil the target noisefigure, by:

-   -   setting, in each remote radio head 3 ₁, 3 ₂ unable to fulfil the        target noise figure, the attenuation of a variable attenuator 6        ₁, 6 ₂ such as to obtain a maximum achievable attenuation, and    -   adding, in the intermediate radio unit 2 ₁, additional noise        such as to obtain the target noise figure.

In a variation of the above embodiment, the distributed antenna systemnetwork 1 is operative to add generated frequency band specific noise.

In variations of the above two embodiments, the distributed antennasystem network 1 is operative to, for the case of one or more remoteradio heads 3 ₁, 3 ₂ being unable to fulfil the target noise figure:

-   -   send, from the remote radio head 3 ₁, 3 ₂ being unable to fulfil        the target noise figure, a message to the intermediate radio        unit 2 ₁ informing about this inability.

In an embodiment, the establishing of the target noise figure isperformed in a control unit 5 or in the intermediate radio unit 2 ₁.

In an embodiment, the uplink noise figure and gain is controlled byadapting the uplink noise figure and gain in view of the number ofactive remote radio heads 3 ₁, 3 ₂.

FIG. 8 illustrates schematically a device 2 ₁, 3 ₁, 5 of a distributedantenna system network land means for implementing embodiments of themethods of the present disclosure. The method 20 as described withreference to FIG. 7 may be performed in the device, which device may bethe control unit 5, the intermediate radio unit 2 ₁ or the remote radiohead. The device 2 ₁, 3 ₁, 5 comprises a processor 30 comprising anycombination of one or more of a central processing unit (CPU),multiprocessor, microcontroller, digital signal processor (DSP),application specific integrated circuit etc. capable of executingsoftware instructions stored in a memory 31, which can thus be acomputer program product 31. The processor 30 can be configured toexecute any of the various embodiments of the method as described inrelation to FIG. 7.

When the device, in which the method 20 is performed, is the controlunit 5, the control unit 5 may establish the target noise figure e.g. bybeing configured with it by the operator. The control unit 5 mayretrieve the target noise figure from a memory. The control unit 5 maythen adjust (e.g. add) attenuation, for each link 4 ₁, 4 ₂ between theone or more remote radio heads 3 ₁, 3 ₂ and the intermediate radio unit2 ₁, such as to obtain the target noise figure for each remote radiohead 3 ₁, 3 ₂ connected to the at least one intermediate radio unit 2 ₁.This can be accomplished by the control unit 5 instructing theintermediate radio unit 2 and/or each remote radio head 3 ₁, 3 ₂ toadjust the attenuation accordingly.

When the device, in which the method 20 is performed, is theintermediate radio unit 2 ₁ the intermediate radio unit 2 ₁ mayestablish the target noise figure e.g. by being configured with it bythe operator or by receiving the target noise figure from the controlunit 5. The intermediate radio unit 2 ₁ may then adjust (e.g. add)attenuation, for each link 4 ₁, 4 ₂ between the one or more remote radioheads 3 ₁, 3 ₂ and the intermediate radio unit 2 ₁, such as to obtainthe target noise figure for each remote radio head 3 ₁, 3 ₂ connected tothe at least one intermediate radio unit 2 ₁. This can be accomplishedby the intermediate radio unit 2 ₁ itself adjusting (e.g. adding)attenuation and/or by instructing the each remote radio head 3 ₁, 3 ₂ toadjust the attenuation accordingly.

When the device, in which the method 20 is performed, is the remoteradio head 3 ₁, 3 ₂, the remote radio head 3 ₁, 3 ₂ may establish thetarget noise figure e.g. by receiving the target noise figure from thecontrol unit 5 or from the intermediate radio unit 2 ₁. The remote radiohead 3 ₁, 3 ₂ may then adjust (e.g. add) attenuation, for each link 4 ₁,4 ₂ between the one or more remote radio heads 3 ₁, 3 ₂ and theintermediate radio unit 2 ₁, such as to obtain the target noise figurefor each remote radio head 3 ₁, 3 ₂ connected to the at least oneintermediate radio unit 2 ₁. This can be accomplished by remote radiohead 3 ₁, 3 ₂ itself adjusting (e.g. adding) attenuation and/or bycommunicating with the intermediate radio unit so that it adjusts anyadditional attenuation needed.

A device 5, 3 ₁ 2 ₁ of a distributed antenna system network 1 is thusprovided. The device 5, 3 ₁ 2 ₁, is configured for controlling an uplinknoise figure and comprising:

at least one processor 30; andat least one memory 31 storing instructions that, when executed by theat least one processor 30, causes the device 5, 3 ₁ 2 ₁, to:

-   -   establish a target noise figure, and    -   adjust, for a link 4 ₁, 4 ₂ between a remote radio head 3 ₁, 3 ₂        and an intermediate radio unit 2 ₁, attenuation such as to        obtain the target noise figure for the remote radio head 3 ₁, 3        ₂ connected to the intermediate radio unit 2 ₁.

Still with reference to FIG. 8, the memory 31 can be any combination ofread and write memory (RAM) and read only memory (ROM). The memory 31also comprises persistent storage, which, for example, can be any singleone or combination of magnetic memory, optical memory, solid statememory or even remotely mounted memory.

A data memory 34 may also be provided for reading and/or storing dataduring execution of software instructions in the processor 30. The datamemory 34 can be any combination of read and write memory (RAM) and readonly memory (ROM).

The present disclosure also encompasses a computer program product 31comprising a computer program 32 for implementing the methods asdescribed above, and a computer readable means on which the computerprogram 32 is stored. The computer program product 31 may be anycombination of read and write memory (RAM) or read only memory (ROM).The computer program product 33 may also comprise persistent storage,which for example can be any single one or combination of magneticmemory, optical memory or solid state memory.

The present disclosure thus comprises a computer program 32 for a device5, 2 ₁, 3 ₁ of a distributed antenna system network 1. The device 5, 2₁, 3 ₁ is configured for adapting an uplink noise figure. The computerprogram 32 comprises computer program code, which, when run on thedevice 5, 2 ₁, 3 ₁ causes the device 5, 2 ₁, 3 ₁ to:

-   -   establish a target noise figure, and    -   adjust, for a link 4 ₁, 4 ₂ between a remote radio head 3 ₁, 3 ₂        and an intermediate radio unit 2 ₁, attenuation such as to        obtain the target noise figure for the remote radio head 3 ₁, 3        ₂ connected to the intermediate radio unit 2 ₁.

The computer program product, or the memory, thus comprises instructionsexecutable by the processor. Such instructions may be comprised in acomputer program, or in one or more software modules or functionmodules.

FIG. 9 illustrates a flow chart over steps of a method in a distributedantenna system network 1 in accordance with the present disclosure. Asdescribed earlier, the method may be performed in a single device of thedistributed antenna system network 1. In an embodiment, a method 40 forcontrolling an uplink noise figure in a distributed antenna systemnetwork 1 is provided. The distributed antenna system network 1comprises at least a first intermediate radio unit 2 ₁ and one or moreremote radio heads 3 ₁, 3 ₂ connected via a respective cable 4 ₁, 4 ₂ tothe at least first intermediate radio unit 2 ₁. If the distributedantenna system network 1 comprises several intermediate radio units, forexample also a second intermediate radio unit 2 ₂, then the one or moreremote radio heads 3 ₁, 3 ₂ may be connected via a respective link(cable) also to this second intermediate radio unit 2 ₂. The method 40comprises:

-   -   establishing 4 ₁ a target noise figure,    -   determining 4 ₂, for each remote radio head 3 ₁, 3 ₂, whether        the established target noise figure can be fulfilled; and        -   for the case of each of the one or more remote radio heads 3            ₁, 3 ₂ being able to fulfil the target noise figure            adjusting (e.g. adding) 43 in each remote radio head 3 ₁, 3            ₂ attenuation such as to obtain the target noise figure, and        -   for the case of one or more remote radio heads 3 ₁, 3 ₂            being unable to fulfil the target noise figure sending 44,            from the remote radio head 3 ₁, 3 ₂ being unable to fulfil            the target noise figure, a message to the intermediate radio            unit 2 ₁ informing about this inability. The attenuation may            then be provided by the intermediate radio unit 2 ₁ or by            providing as much attenuation as possible by the remote            radio heads 3 ₁, 3 ₂ and adding the remaining part in the            intermediate radio unit 2 ₁ or by adjusting the target noise            figure and then provide as much attenuation as possible by            the remote radio heads 3 ₁, 3 ₂ and add the remaining part            in the intermediate radio unit 2 ₁.

FIG. 10 illustrates a device of a distributed antenna system network 1comprising function modules/software modules for implementing methods ofthe present disclosure. An example of an implementation using functionmodules/software modules is illustrated in FIG. 10, in particularillustrating a device 5, 2 ₁, 3 ₁ of a distributed antenna systemnetwork 1 comprising function modules for implementing embodiments ofthe methods of the present disclosure. The device 5, 2 ₁, 3 ₁ comprisesfirst means 50, for instance a first function module, for establishing atarget noise figure. The device 5, 2 ₁, 3 ₁ comprises second means 51,for instance a second function module, for adjusting, for a link 4 ₁, 4₂ between a remote radio head 3 ₁, 3 ₂ and an intermediate radio unit 2₁, attenuation such as to obtain the target noise figure for the remoteradio head 3 ₁, 3 ₂ connected to the intermediate radio unit 2 ₁.

The device may comprise yet additional such means (not illustrated) forimplementing the various steps and features of the present disclosure.

The function modules 50, 51 can be implemented using softwareinstructions such as computer program executing in a processor and/orusing hardware, such as application specific integrated circuits, fieldprogrammable gate arrays, discrete logical components etc.

The invention has mainly been described herein with reference to anumber of embodiments. However, as is appreciated by a person skilled inthe art, other embodiments than the particular ones disclosed herein areequally possible within the scope of the invention, as defined by theappended patent claims.

1. A method for controlling an uplink noise figure and gain in adistributed antenna system network comprising at least one intermediateradio unit and one or more remote radio heads connected via a respectivelink to the at least one intermediate radio unit, the method comprising:establishing a target noise figure, and adjusting, for each link betweenthe one or more remote radio heads and the intermediate radio unit,attenuation such as to obtain the target noise figure for each remoteradio head connected to the at least one intermediate radio unit.
 2. Themethod as claimed in claim 1, wherein the establishing the target noisefigure comprises: measuring in each remote radio head a respective cableattenuation and reporting it to the intermediate radio unit,establishing, in the intermediate radio unit, the highest cableattenuation among the received reports about measured cableattenuations, and establishing the target noise figure to be equal to anoise figure corresponding to the noise figure of the link having thehighest cable attenuation.
 3. The method as claimed in claim 1, whereinthe establishing the target noise figure comprises: measuring in theintermediate radio unit a respective cable attenuation, establishing, inthe intermediate radio unit, the highest cable attenuation among themeasured cable attenuations, and establishing the target noise figure tobe equal to a noise figure corresponding to the noise figure of the linkhaving the highest cable attenuation.
 4. The method as claimed in claim1, comprising, after the establishing of the target noise figure andbefore the adjusting: determining, for each remote radio head, whetherthe established target noise figure can be fulfilled for the respectiveremote radio head.
 5. The method as claimed in claim 4, wherein theadjusting comprises for the case of each of the one or more remote radioheads being able to fulfil the target noise figure: adding, in eachremote radio head, attenuation such as to obtain the target noisefigure.
 6. The method as claimed in claim 4, comprising for the case ofone or more remote radio heads being unable to fulfil the target noisefigure: setting, in each remote radio head unable to fulfil the targetnoise figure, the attenuation of a variable attenuator such as to obtaina maximum achievable attenuation, and adding, in the intermediate radiounit, additional noise such as to obtain the target noise figure.
 7. Themethod as claimed in claim 6, wherein the adjusting comprises addinggenerated frequency band specific noise.
 8. The method as claimed inclaim 4, comprising for the case of one or more remote radio heads beingunable to fulfil the target noise figure: sending, from the remote radiohead being unable to fulfil the target noise figure, a message to theintermediate radio unit informing about this inability.
 9. The method asclaimed in claim 1, wherein the establishing of the target noise figureis performed in a control unit or in the intermediate radio unit. 10.The method as claimed in claim 1, wherein the method is performed in theone or more remote radio heads and wherein the establishing the targetnoise figure comprises receiving, from a control unit or from the anintermediate radio unit, the target noise figure.
 11. The method asclaimed in claim 1, wherein the method is performed in the distributedantenna system network.
 12. The method as claimed in claim 1, whereinthe uplink noise figure and gain is controlled by adapting the uplinknoise figure and gain in view of the number of active remote radioheads.
 13. The method as claimed in claim 1, wherein the adjusting isperformed such as to obtain the target noise figure and linearity foreach remote radio head connected to the at least one intermediate radiounit.
 14. A distributed antenna system network comprising at least oneintermediate radio unit and one or more remote radio heads connected viaa respective link to the at least one intermediate radio unit, thedistributed antenna system network being configured for controlling anuplink noise figure and comprising: at least one processor; and at leastone memory storing instructions that, when executed by the at least oneprocessor, causes the distributed antenna system network: establish atarget noise figure, and adjust, for each link between the one or moreremote radio heads and the intermediate radio unit, attenuation such asto obtain the target noise figure for each remote radio head connectedto the at least one intermediate radio unit.
 15. The distributed antennasystem network as claimed in claim 14, operative to establish the targetnoise figure by: measuring in each remote radio head a respective cableattenuation and reporting it to the intermediate radio unit,establishing, in the intermediate radio unit, the highest cableattenuation among the received reports about measured cableattenuations, and establishing the target noise figure to be equal to anoise figure corresponding to the noise figure of the link having thehighest cable attenuation.
 16. The distributed antenna system network asclaimed in claim 14, operative to establish the target noise figure by:measuring in the intermediate radio unit a respective cable attenuation,establishing, in the intermediate radio unit, the highest cableattenuation among the measured cable attenuations, and establishing thetarget noise figure to be equal to a noise figure corresponding to thenoise figure of the link having the highest cable attenuation.
 17. Thedistributed antenna system network as claimed in claim 14, operative to,after the establishing of the target noise figure and before theadjusting: determine, for each remote radio head, whether theestablished target noise figure can be fulfilled for the respectiveremote radio head.
 18. The distributed antenna system network as claimedin claim 17, operative to adjust, for the case of each of the one ormore remote radio heads being able to fulfil the target noise figure,by: adding, in each remote radio head, attenuation such as to obtain thetarget noise figure.
 19. The distributed antenna system network asclaimed in claim 17, operative to for the case of one or more remoteradio heads being unable to fulfil the target noise figure: setting, ineach remote radio head unable to fulfil the target noise figure, theattenuation of a variable attenuator such as to obtain a maximumachievable attenuation, and adding, in the intermediate radio unit,additional noise such as to obtain the target noise figure.
 20. Thedistributed antenna system network as claimed in claim 19, operative toadd generated frequency band specific noise.
 21. The distributed antennasystem network as claimed in claim 17, operative to for the case of oneor more remote radio heads being unable to fulfil the target noisefigure: send, from the remote radio head being unable to fulfil thetarget noise figure, a message to the intermediate radio unit informingabout this inability.
 22. The distributed antenna system network asclaimed in claim 14, wherein the establishing of the target noise figureis performed in a control unit or in the intermediate radio unit. 23.The distributed antenna system network as claimed in claim 14, whereinthe uplink noise figure and gain is controlled by adapting the uplinknoise figure and gain in view of the number of active remote radioheads.
 24. A device of a distributed antenna system network, the devicebeing configured for controlling an uplink noise figure and comprising:at least one processor; and at least one memory storing instructionsthat, when executed by the at least one processor, causes the device to:establish a target noise figure, and adjust, for a link between a remoteradio head and an intermediate radio unit, attenuation such as to obtainthe target noise figure for the remote radio head connected to theintermediate radio unit.
 25. A computer program for a device of adistributed antenna system network, the device being configured foradapting an uplink noise figure, the computer program comprisingcomputer program code, which, when run on the device causes the deviceto: establish a target noise figure, and adjust, for a link between aremote radio head and an intermediate radio unit, attenuation such as toobtain the target noise figure for the remote radio head connected tothe intermediate radio unit.
 26. A computer program product comprising acomputer program as claimed in claim 25, and a computer readable meanson which the computer program is stored.